This invention relates to epoxy resin compositions. In one aspect, the invention relates to the preparation of low-stress epoxy resin compositions useful in encapsulating electrical components.
Epoxy resins are used to encapsulate electrical components such as integrated circuits. The optimum properties for encapsulation resins include low melting point in the uncured state (to permit encapsulation of the component at a relatively low temperature), high glass transition temperature in the cured state (to permit encapsulation of a component which can tolerate high operating temperatures), low modulus and low coefficient of thermal expansion of the cured resin (properties related to the ability of the cured resin to resist "stress" or cracking at high operating temperatures, which results in damage to the semiconductive elements) and fast cure (to permit maximum speed and productivity in assembly).
One class of epoxy resin used in electrical encapsulation is epoxidized orthocresol novolac (EOCN) resins. EOCN resins have high glass transition temperatures and good moisture resistance, but they are subject to "stress" or cracking under high operating temperatures.
Another class of epoxy resins suitable for electrical encapsulation are diglycidyl ether of 4,4'-dihydroxybiphenyls. These epoxy resins have the highly desirable property of low modulus, which is an indication of the ability of the cured resin to resist cracking during high temperature use. However, for some encapsulation applications, the softening point of the resin is undesirably high. Furthermore, the melt viscosity is quite low, which can result in flashes when the resin is subjected to transfer molding operations.
It is therefore an object of the invention to provide an epoxy resin suitable for electrical encapsulation applications. In a specific aspect, it is an object to provide a low-modulus encapsulation formulation which has a reduced tendency to flash during transfer molding.